Hi all, I’m currently in the process of adding fill dirt to build a raised house pad (4 feet above grade at some places). The fill dirt was excavated from a neighbor’s project and looks fine to me but then again it’s not engineered fill. Assuming it compacts well and seems to have sufficient bearing capacity (according to a pocket penetrometer, for example), can I build footings directly on this house pad (and backfill to establish the grade level afterwards)?
I am being told by the excavation contractor that I still need to trench all the way to hard pan and build a wall up from there. This would result in more concrete than I hoped (as frost depth in my area is only 12”) and would not be in keeping with my goal of reduced carbon.
Under what circumstances would an inspector require compaction testing by an engineer?
If trenching to hard pan is required, can I reducing the amount of concrete by partially filling the trench with compacted engineered fill and pour footings on top of that?
Thanks! Adam (zone 4 marine, frost depth 12”)
Replies
If you're hoping to use the prescriptive provisions of the International Residential Code (IRC), your options are building on engineered fill or digging down to undisturbed soil. If you want to go the engineered route (find your own solution outside of what the IRC provides), then they'll need to do soil testing. The circumstances requiring testing of fill for supporting footings and foundations are basically: if it's fill, it needs to be tested, full stop. The code requirement for this is R401.2 in the 2021 IRC (might be the same or different provision in the same chapter of earlier versions, if your jurisdiction hasn't adopted the latest IRC). https://codes.iccsafe.org/content/IRC2021P1/chapter-4-foundations
Thanks Matt,
So if I go with the prescriptive path, does the entire house pad need to be engineered fill? Or can I just trench where the footings are to be located and fill there (creating a stable bearing surface under the footing, and extending past at 45 degrees to sides of the footing)?